1. Field of the Invention
The present invention relates to a keyboard apparatus which can prevent unstable factors such as gradient, shake, rotation, and the like of quadrangular key buttons.
2. Related background art
A conventional keyboard apparatus is shown in FIGS. 1 to 23. First, a first conventional structure will be described with reference to FIGS. 1 to 7.
FIGS. 1 and 2 show an electronic desk calculator (hereinafter, abbreviated as an electronic calculator) as an example of an electronic equipment in which a keyboard apparatus is used.
An electronic calculator 101 has an upper casing 102 and a lower casing 103. The front half portion of the upper surface of the upper casing 102 (panel) serves as a keyboard section 104. The keyboard section 104 consists of a number of key buttons 105. A solar battery 106 and a display device 107 are also provided.
As shown in FIG. 1, a keyboard such as keyboard section 104 is filled with a number of key buttons 105 is called a full keyboard type keyboard.
As well as such a full keyboard type keyboard, there is also a keyboard of the type having a plurality of key buttons as shown in FIG. 2. In many cases, the keyboard as shown in FIG. 2 has a structure such that the respective key buttons are inserted from the upper side of the upper casing 102.
In the case of such a structure, the key buttons need to freely descend and ascend and at the same time, a slip-out preventing structure of the key button is also necessary.
FIGS. 3 to 5 show the first example of the key buttons provided with such a slip-out preventing mechanism.
Namely, the key button 105 is formed like A square plate. a prismatic guide axis 108 is projected from the lower surface of the key button 105. The guide axis 108 is slidably inserted into an opening portion 109 formed in the bottom surface of a recess portion 110 adapted to accommodate the key button of the upper casing 102.
On the other hand, retaining claws 111 and 112 are projected from the bottom surface of the key button 105 at the end portions substantially along a diagonal of the key button. Hooks 111a and 112a are outwardly projected from the lower end portions of the retaining claws 111 and 112.
The claws 111 and 112 are elastically deformed and inserted into guide holes 113 formed in the bottom surface of the recess portion 110 as so to sandwich the opening portion 109.
When the hooks 111a and 112a pass through the guide holes 113, the upper surfaces of those hooks are retained by notched portions 102a formed on the side of the lower surface of the upper casing 102 as shown in FIGS. 4 and 5, respectively.
A printed circuit board 114 is arranged on the side of the bottom surface of the upper casing 102 as shown in FIGS. 4 and 5. A key pattern 115 is formed on the printed circuit board 114 so as to face the guide axis 108.
An elastic rubber plate 116 is disposed on the board 114. The rubber plate 116 is formed with an expanded portion 116a having a trapezoidal cross section in correspondence to the guide axis 108. A conductive rubber 117 is fixed to the lower surface of the expanded portion 116a.
In the keyboard apparatus having the structure mentioned above, when none of the key buttons 105 is pressed, each key button 105 is upwardly pressed due to the elastic force of the expanded portion 116a so that the conductive rubber 117 is apart from the key pattern 115.
On the contrary, when the key button 105 is pressed, the expanded portion 116a is elastically deformed, so that the conductive rubber 117 comes into contact with the key pattern 115 and a key signal can be input.
When using the above-mentioned keyboard structure, for instance, in order to smoothly descend and ascend along the guide axis 108, clearance is required between the opening portion 109 and the peripheral surface of the guide axis 106.
When such a key button 105 is pressed, if it is pressed at either one of the positions corresponding to the retaining claws 111 and 112 as indicated at reference numerals 111b and 112b in FIG. 3, a slight force f will be applied to this position as shown in FIG. 6. However, in this case, an amount of inclination of the key button 105 will be small since the retaining claws 111 and 112 also serve as guide members. On the contrary, as shown at reference characters X and Y in FIG. 3, if the force f is applied to either one of the positions where the retaining claws 111 and 112 are not formed, the opposite side on the diagonal line will be greatly lifted up.
Thus, as shown in FIG. 7, there is the drawback such that the key button 105 is greatly inclined and shaken.
A second conventional structure will now be described with reference to FIGS. 8 to 14.
FIGS. 8 to 10 show a second example of key buttons equipped with a slip-out preventing mechanism as a modified form of FIGS. 3 to 5 mentioned above.
Namely, a key button 205 is formed like a square plate. A prismatic guide axis 208 is projected from the lower surface of the key button 205. The guide axis 208 is slidably inserted into an opening portion 209 formed in the bottom surface of a recess portion 210 adapted to accommodate the key button of the upper casing 202.
In addition, retaining claws 211 and 212 project from the bottom surface of the key button 205 at the edge portions substantially along a diagonal of the key button. Hooks 211a and 212a outwardly project from the lower end portions of the retaining claws 211 and 212.
The claws 211 and 212 are elastically deformed and inserted into guide holes 213 formed in the bottom surface of the recess portion 210 so as to sandwich the opening portion 209.
When the hooks 211a and 212a pass through the guide holes 213, the upper surfaces of the hooks are retained by notched portions 202a formed on the side of the lower surface of the upper casing 202 (panel) as shown in FIGS. 9 and 10, respectively.
A printed circuit board 214 is arranged on the side of the bottom surface of the upper casing 202 as shown in FIGS. 9 and 10.A key pattern 215 is formed on the printed circuit board 214 so as to face the guide axis 208.
On the other hand, an elastic rubber plate 216 is disposed over the board 214. The rubber plate 216 is formed with an expanded portion 216a having a trapezoidal cross section in correspondence to the guide axis 208. A conductive rubber 217 is fixed to the lower surface of the expanded portion 216a.
In the keyboard apparatus having the structure mentioned above, when none of the key buttons 205 is pressed, each key button 205 is upwardly pressed due to the elastic force of the expanded portion 216a so that the conductive rubber 27 is away from the key pattern 215.
On the contrary, when the key button 205 is pressed, the expanded portion 216a is elastically deformed, so that the conductive rubber 217 comes into contact with the key pattern 215 and a key signal can be input.
When using the above-mentioned keyboard structure, for instance, in order to smoothly descend and ascend along the guide axis 208, a clearance is required between the opening portion 209 and the peripheral surface of the guide axis 206.
Therefore, if a slight force f is applied to one end of the key button 205 as shown in FIG. 11, a rotational motion will occur in the key button 205 around the contact portion between the upper surface of the notched portion 202a and one end 212b of the hook 212a as a rotational center.
Thus, when the right end of the key button 205 descends by a distance .alpha., the left end is contrarily lifted up by only a distance .beta. as shown in FIG. 11.
In the case shown in FIG. 11, there is the relation of .alpha.&gt;.beta. since the hook 212a is located at nearly the intermediate position between the guide axis 208 and the edge of the key button 205.
On the other hand, when the hook 212a is located near the side of the guide axis 208 as shown in FIG. 12, when the right end side of the key button descends by only the distance .alpha., the left end is lifted up by a distance .gamma., so that there is the relation of .gamma.&gt;.beta..
In such a case, the key button will also greatly shake.
Therefore, to prevent such a shake, there has been proposed the structure in which the hook 212a is formed at the maximum distance away from the guide axis 208 as shown in FIGS. 13 and 14.
When such a structure is used, even if the force f is applied to the right end side of the key button and this side accordingly descends by a distance .alpha. as shown in FIG. 13, the portion at a left end A won't be lifted up, so that the shaking motion of the key button will be reduced.
However, electronic equipment provided with the keyboard has been more and more miniaturized and both the keyboard and the key buttons have also been miniaturized in association with it. Thus, even if the hook portion is formed at the maximum distance away from the guide axis, the effect to reduce the shaking motion of the key button will be small.
There is also the drawback such that an increase in size of the button obstructs the miniaturization of the whole keyboard apparatus.
The third conventional structure will now be described with reference to FIGS. 15 to 23.
Such a conventional apparatus has the structure such that a part (e.g., 301a in FIG. 15) of the outer periphery of the key button, an outer peripheral surface (e.g., 307a in FIG. 17) of the axial portion formed integrally with the key button, or an outer peripheral surface (e.g., FIG. 21) of a slide part of a key button unit integrally formed from a plurality of members can slide with a part of an inner peripheral surface of an opening portion of a supporting member (a part of a casing is commonly used as this supporting member) which faces this outer peripheral slide surface. The position in the lateral direction in the opening portion of the supporting member of the key button is controlled due to each of those slide surfaces.
FIGS. 15 to 23 illustrate different practical conventional examples, respectively.
In the example shown in FIGS. 15 and 16, each side surface of a key button 301 serves as the slide surface 301a adapted to be slidable between the key button 301 and the supporting member. A flange 301b, also serving as a stopper to determine the top dead point of the key button, is formed on the lower end of the key button 301.
A supporting member (panel) 302 is provided as part of the casing. An inner surface of an opening portion into which the key button 301 is inserted functions as a sliding surface 302a of the key button. A surface 302b on the lower side of the peripheral surface of the opening portion is the surface to determine the top dead point of the key button.
An elastic member 303 consisting of flexible rubber or the like is arranged under the key button, thereby lifting up the key button. A conductive member 303a is integrally formed on the lower surface of the head portion of the elastic member 303.
A key pattern 305 is formed on a base plate 304.
In the above structure, the sliding clearance of dimension "a" is required between the slide surface 301a of the key button and the sliding surface 302a of the supporting member.
FIGS. 17 to 19 show another conventional example of a unit structure. Reference numeral 306 denotes a key button and 307 indicates a slide part pressure inserted into the key button 306. The side surface of the slide part 307 serves as the slide surface 307a.
As shown in the enlargement in FIG. 18, a projecting portion 307b having a right-angled triangular cross section is formed in the lower end portion on the outside of the slide surface 307a. The upper surface of the projecting portion 307b functions as an abutting surface of the portion to determine the top point of the slide part 307 against the supporting member.
Numeral 308 denotes a supporting member, 308a is a slide surface of the supporting member 308, and 308b is a supporting member surface to decide the top dead point of the slide part 307.
In addition, numeral 309 denotes a spring to lift up the key button unit and make the lower flexible base plate operative; 310 is a flexible base plate having a pattern 314 on the back side surface; 311 is a flexible base plate having a pattern 315 on the front side surface; 312 is a spacer interposed between the flexible base plates 310 and 311; 313 is a reinforcing plate to support the flexible base plates; and 314 and 315 are the key patterns.
When using the above-mentioned structure, a clearance "b" which provides a vertical slide motion is required between the slide surface 307a of the slide part of the key button unit and the slide surface 308a of the supporting member.
In the example shown in FIGS. 20 and 21, numeral 316 denotes a key button; 316a is a key button slide surface; and 317 is a side wall formed integrally with the key button 316 and serving as a slide surface. The outside of the lower end of the side wall 317 is formed with a projection 317a which determines the top dead point of the key button.
Numeral 318 denotes a supporting member and a cylindrical body 318a adapted to guide the slide surface 316a is formed as part of the supporting member 318. The inner peripheral surface of the supporting member 318 functions as a slide surface.
Numeral 318b denotes a supporting member surface to determine the top dead point of the key button 316; 319 is a flexible rubber to lift up the key button; 320 is a conductive member formed integrally with the flexible rubber 319; 321 is a base plate; and 322 is a key pattern section formed on the base plate 321.
When such a structure is used, a clearance of a dimension "c" is necessarily formed between the slide surface 316a of the key button and the slide surface 318a of the supporting member.
As described in the foregoing three conventional examples, a clearance is necessarily required between the slide surface of the key button and the slide surface of the supporting member and a shaking motion occurs due to this clearance in the conventional examples.
Thus, inclination, rotation, or eccentricity of a key button as shown in FIGS. 22 and 23 inevitably occurs. Therefore, there is the large drawback from the viewpoints of external appearance and quality.